Hello again,
Can you posts pic's of amp?
Do you have an oscilloscope?
If you can identify the LM361, I don't recall the locator,but it is in the center of the drive section and the part number may be scraped off. If so measure DC volts around chip and post results.
I will review schematics tomorrow
Can you posts pic's of amp?
Do you have an oscilloscope?
If you can identify the LM361, I don't recall the locator,but it is in the center of the drive section and the part number may be scraped off. If so measure DC volts around chip and post results.
I will review schematics tomorrow
U14 is the chip I was referring to in previous post.
Measure the frequency w/o signal at the input to the output coils with one probe on neg spkr terminal (black or red probe is not important since you will be using the AC function), should be 80Khz.
If you are able to measure duty cycle you should see a 50% duty cycle, if you then apply signal using a 100hz test tone you will see the duty cycle vary slightly as you turn volume control through it's range. Or you can measure the frequency on the output of output coils which should be 100hz if the class D circuit and outputs are passing a modulated drive.
This may be premature, so only if you have modulated drive to the coils and coils are not open, which is not likely to have two open coils the signal is not passing through the relay. Which means the relay contacts are corroded or pitted, bad or cold solder or relay turn on circuit is bad.
Do you hear the relay click ? Is there approx. 14 volt drop across D92 when amp is fully powered up?
Measure the frequency w/o signal at the input to the output coils with one probe on neg spkr terminal (black or red probe is not important since you will be using the AC function), should be 80Khz.
If you are able to measure duty cycle you should see a 50% duty cycle, if you then apply signal using a 100hz test tone you will see the duty cycle vary slightly as you turn volume control through it's range. Or you can measure the frequency on the output of output coils which should be 100hz if the class D circuit and outputs are passing a modulated drive.
This may be premature, so only if you have modulated drive to the coils and coils are not open, which is not likely to have two open coils the signal is not passing through the relay. Which means the relay contacts are corroded or pitted, bad or cold solder or relay turn on circuit is bad.
Do you hear the relay click ? Is there approx. 14 volt drop across D92 when amp is fully powered up?
![20160118_211231[1].jpg](/community/data/attachments/478/478476-1addb92e8f7bf220f065934eb2762f79.jpg)
Ground pin 3 and check for 80khz at pin 11.
To ground pin 3 tack solder a small gauge wire from pin 3 to other side of C270. To be sure which side is correct an ohmmeter from one side of cap to neg spkr term should read shorted.
If this yields 80khz at pin 11, then U14 is good and replacing U11 TLO72 should fix problem, otherwise replace U14 LM361
To ground pin 3 tack solder a small gauge wire from pin 3 to other side of C270. To be sure which side is correct an ohmmeter from one side of cap to neg spkr term should read shorted.
If this yields 80khz at pin 11, then U14 is good and replacing U11 TLO72 should fix problem, otherwise replace U14 LM361
replaced u11 with a known working one because i didn't have any new ones in stock. fired the amp up with a speaker in place, inputs plugged in and all i get is a touch of static on the bass hits of the music, silence between bass hits. gain up or down, xover up or down and bass up or down changes nothing. lm361 was already replaced with new also, it was the first thing i did.
You may want to replace U11 with a fresh TLO72
Check and reflow solder to all parts replaced, particularly IC's and transistor drivers.
There are 5 resistors and 1 inductor that should be checked. For Q113,135-A1381 they are 1 ohm,120 ohm,2k ohm,910 ohm,180 ohm. For Q104,126-C3503 they are 1 ohm,220 ohm,2k ohm,910 ohm,180 ohm.
L101,102,103,104 can be checked with an ohmmeter and as long as they are a couple of ohms they should be good.
Do the Zener diodes you replaced all have a 12 volt drop across them?
I realize you may have done all this, but it's easy to overlook something, especially in this complex circuit. If U11 is in fact good and we know that the U14 is based on grounding Pin 3 test you performed, it's hard to pin down the problem, because it lies in the feedback loop, such as bad solder, broken trace or a defective replacement part.
Check and reflow solder to all parts replaced, particularly IC's and transistor drivers.
There are 5 resistors and 1 inductor that should be checked. For Q113,135-A1381 they are 1 ohm,120 ohm,2k ohm,910 ohm,180 ohm. For Q104,126-C3503 they are 1 ohm,220 ohm,2k ohm,910 ohm,180 ohm.
L101,102,103,104 can be checked with an ohmmeter and as long as they are a couple of ohms they should be good.
Do the Zener diodes you replaced all have a 12 volt drop across them?
I realize you may have done all this, but it's easy to overlook something, especially in this complex circuit. If U11 is in fact good and we know that the U14 is based on grounding Pin 3 test you performed, it's hard to pin down the problem, because it lies in the feedback loop, such as bad solder, broken trace or a defective replacement part.
BTW, Q105-108,Q114-117,Q127-130,Q136-139 should be checked with an ohmmeter. compare one bank to another and if you see any discrepancies, you should change all 4 sm transistors in a bank. Each bank consists of two KTC4373y's and two KTA1661y's.
Also, It occurred to me that one of the output mosfets maybe be weak or open. You may be able to detect with an ohmmeter, but you should remove outputs and see if the LM361 is outputting 80khz and if its getting through the drivers to the gate resistors. You can do this one bank at a time to save on parts, or remove all at once and replace with fresh batch matched mosfets.This would be my choice.
Hang in there!!
Also, It occurred to me that one of the output mosfets maybe be weak or open. You may be able to detect with an ohmmeter, but you should remove outputs and see if the LM361 is outputting 80khz and if its getting through the drivers to the gate resistors. You can do this one bank at a time to save on parts, or remove all at once and replace with fresh batch matched mosfets.This would be my choice.
Hang in there!!
The 3.3kohm 5w resistors next to D108 & D121 should have the -rail voltage on one side. To illustrate look at the the two 3.3kohm resistors feeding D107,D120. The voltage on one side will be the + rail (71volts with a 14.4 battery term voltage) the other side will be 12volts less or approx 59 volts,using the transformer center tap.
Okay, so the reason why you are not seeing the 12 volt drop across D108,D121 is either two open resistors (not likely) or the -rail is missing. Dollars to Doughnuts you have broken leg/s on the power supply filter inductor. Fairly common issue with this amp. If this is the case, you may be able to stuff leg/s back in board and resolder.Keep your fingers crossed.
Okay, so the reason why you are not seeing the 12 volt drop across D108,D121 is either two open resistors (not likely) or the -rail is missing. Dollars to Doughnuts you have broken leg/s on the power supply filter inductor. Fairly common issue with this amp. If this is the case, you may be able to stuff leg/s back in board and resolder.Keep your fingers crossed.
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